To mount the calliper, I know I probably need to have the mechanic drill and weld the nut to the swing arm if I want to achieve standard look, or I could buy a bracket (ugly)
Or should I buy 5S swing arm?
I was afraid new swing arm requires me to buy a new hugger too. It's not gonna stop there.

And how to securely mount the master cylinder to the chassis?

The above parts already cost me RM500+ but my emphasis is safety and I don't want to skimp on it. I know I could get a local one cost like RM200. Not gonna risk it though.
Primary focus totally standard indistinguishable 5S rear disc brake look.
Btw I also already have 5S rims